In television, there is an increasing number of shows that bring about viewer participation (or audience participation). For example, in television reality show, the viewer can vote for a candidate or, in a games show he can respond to a quiz. In every case, the television viewer has to give an answer to a question that he is asked during the show. The television viewer is asked the question through least one image that is displayed by the television screen. As a complement or alternatively, the question can be formulated vocally by the presenter of the show and is rendered by the television speakers.
2.1 HBBTV
According to the HBBTV standard, the pieces of additional information to be displayed on the television screen are available directly in the multimedia stream (broadcast information) or else delivered via a connection (return channel) between the user's terminal (the connected television set or set-top box) and a server of the broadcaster or a third party operating in relation with the broadcaster (information transmitted through broadband unicast access). This should ultimately make it possible to cover every use generally offered by connected television: catch-up TV, VOD (video-on-demand), interactive advertising, customizing programs, voting, games, social networks, program guides, etc.
For example, during a cookery show, the viewer can have the recipe displayed on his HBBTV terminal if the information is being streamed by the broadcaster.
An HBBTV terminal (i.e. a terminal compatible with the HBBTV standard) has a software architecture generally comprising a systems software program above which an interactive television middleware program is executed. Within the interactive television middleware program, we can generally distinguish a module for managing interactive applications (including a browser), a module for managing tables and a module for managing object carousels.
During the deployment of a given interactive application associated with a given program (on a television channel), the broadcaster transmits the given program within a multimedia stream, this program comprising:                elementary audio and/or video streams;        tables describing these elementary streams, in particular the PAT (“Program Allocation Table”) and the PMT (“Program Map Table”);        constituent elements (especially a software code, for example in HTML, in the form of a web page) of a given interactive application transmitted for example within an object carousel encoded according to the DSM CC (“Digital Storage Media Command and Control”) standard;        an AIT (Application Information Table) identifying all the interactive applications available for the given program (including a given interactive application) as well as the way in which these interactive applications are available (object carousel in this case for the given interactive application).        
Upon reception of this given program, the HBBTV terminal displays the audio and video streams (through tables that describe them). Besides, within the interactive television middleware program, the table management module processes the AIT table and detects the fact that a software code of the given interactive application has been transmitted in an object carousel. The carousel management module receives and reassembles the constitute elements of the given interactive application and the applications management module manages the given interactive application (reassembled by the carousel management module). Like any interactive application, this application can for example take one of the following states: loaded, paused, active or destroyed.
In one variant of the deployment of a given interactive application, the given (broadcast) program does not include the constituents of the given interactive application but the AIT table specifies a URL address at which the given interactive application can be obtained. Within the interactive television middleware of the HBBTV terminal, we then have the following actions: the table management module processes the AIT table and obtains this URL address; the browser of the applications management module sends a request to this URL address in order to receive the given interactive application; and the applications management module manages the given interactive application.
One drawback of this operation, whatever the deployment mode used, lies in the fact that there is visual discomfort for the user. Indeed whenever, on a given television channel (a program), the user accesses a particular interactive application associated with a program proposing access to a web portal, this leads to the display, as an overlay on the current TV program, of a window containing a message or a logo informing the user that access to a portal is possible by pressing a button (the OK button for example) on the remote control of the HBBTV terminal. Besides, when the user validates access to a portal, he is no longer able to follow the current TV program since he is redirected towards the screens of the portal on his HBBTV terminal.
2.1 “Second-Screen” Applications
There are numerous initiatives by broadcasters and television content producers for the development of services on smartphones or tablets used to provide additional content complementing television programs. These proprietary developments are known as “second-screen applications” and provide contents complementary to the television programs according to the scope (for example for all channels, for one channel or for one program) on a device (for example a smartphone or a tablet) that is distinct from the one used to view the TV program (for example a television set). These additional contents can be editorials or interactive contents (such as quizzes, surveys, predictions, etc.) which may or may not be synchronized with the TV program.
In most cases, synchronization is necessary between the TV stream and the contents displayed on the second-screen application of the second device and can be implemented by several different technologies, among them:                watermarking: this technique consists of the addition of supplementary pieces of information to an audio-visual content enabling the insertion of “markers” into the content. This technique is often used to insert a copyright. It is also used to insert audio markers into the TV stream that are imperceptible to the user but can be captured by the second-screen application to trigger a process or action. Digital watermarking is implemented at the broadcaster level;        digital fingerprinting: this technique consists in generating a file of signatures from an audio-visual content. This file then enables an audio synchronization module listening to a stream (for example on the second device executing the second-screen application), to know the precise position in the content. For example, an audio signature of an episode in a series makes it possible to know the position in the episode in which the viewer is situated. This technique is independent of the broadcaster and is not very reliable because it depends on ambient noise and the quality of reception in the room where the viewer is watching TV;        a technique known as time-stamping: this technique consists in triggering events on the second-screen application only on a time-related basis. This technique is not very reliable and does not enable management of the lags or divergences that could occur between different means for receiving TV streams (IPTV, TNT, satellite, etc.).        
The main drawback of these second-screen applications therefore lies in the lack of reliability or of precision of the synchronization techniques needed for their efficient operation.
A second drawback of these second-screen applications lies in the fact that they are specific to each broadcaster or even to each program and therefore do not allow for any pooling of the technical functions developed for each of them.